Generally, battery-units, in which plural batteries (battery cells) are connected in series, are employed as high output, high capacity battery-units employed for, for example, driving the motors of hybrid automobiles and electric automobiles. Specific examples of such battery-units include lithium ion battery-units. An assembled-battery system is known that measures battery voltages in order to monitor and control the battery voltages of batteries in a battery-unity.
A conventional assembled-battery system of this sort is known in which the battery voltage of each battery cell is measured using the difference between voltage at the high potential side and the voltage at the low potential side of plural battery cells connected together in series. For example, in the technology described by Japanese Patent Application Laid-Open (JPA) No. 2010-16928, (two) terminals out of terminals connected to respective battery cells through power-supply lines are selected by a multiplexer, and output to a differential amplifier. Moreover, in the technology described by JP-A No. 2010-16928, an analog electrical signal output from the differential amplifier is output as a digital electrical signal, and the battery voltage across each battery cell is measured based on the digital electrical signal.
JP-A No. H08-189845 describes a digital measuring device that includes self-diagnostic functionality. As illustrated in FIG. 9, the digital measuring device described in JP-A No. H08-189845 includes a range switching circuit 109 that switches the gain of a single input circuit, and has functionality for performing self-diagnostics of the single input circuit (the range switching circuit 109). In the range switching circuit 109 illustrated in FIG. 9, gain is switched according to whether switching element switches 192, 193 are connected to an NC side or an NO side.
For example, the gain of the range switching circuit 109 is set at gain G1 or gain G2. In the signal input circuit illustrated in FIG. 9, G1×A, which is a value obtained when a reference voltage A is input to the range switching circuit 109 with gain G1, and G2×A, which is a value obtained when the reference voltage A is input to the range switching circuit 109 with gain G2, are AD (analog-to-digital) converted, and a ratio of the gain G1 and the gain G2 is found from the AD converted signal in order to diagnose whether or not gain switching is functioning normally.
SUMMARY OF INVENTION